1. Field of Invention
The present invention is directed to a method and apparatus for detecting moisture. In particular, the preferred embodiments of the present invention provide an optical sensor that can detect raindrops accumulated on a vehicle.
2. Description of Related Arts
In the field of rain sensors, several conventional methods of rain detection currently exist. One conventional method of rain detection is described in U.S. Pat. No. 4,578,995, in which a pair of spaced apart parallel conductive rods are mounted in a housing. The housing has an open slot, through which raindrops may fall and be directed to the area between the two electrodes. If sufficient water accumulates between the two electrodes so as to form a conductive path, an electrical circuit is completed and rain is detected. One disadvantage associated with this type of rain detection method is that during light rain, there may not be sufficient amount of rainfall to form a conductive path between the electrodes.
Another conventional method of rain detection, disclosed in U.S. Pat. No. 4,584,508, consists of a rain sensor that includes a vibrator, the outer surface of which is exposed to potential raindrops. Upon experiencing rain drops on the outer surface, the vibrator oscillates at an amplitude and frequency corresponding to the energy applied by the raindrops. The rain sensor is adapted to produce rain condition indicative signals corresponding to the oscillation amplitude of the vibrator. One major disadvantage associated with this type of system is that the outer surface of the vibrator must be sufficiently large to xe2x80x9ccatchxe2x80x9d raindrops, making the detector unsightly. Another disadvantage associated with this detection method is that light rain or mist may not contain raindrops with enough mass to cause sufficient impact on the vibrator to be detected.
U.S. Pat. No. 4,987,296 discloses another type of conventional rain detection method whereby a light beam is projected from a transmitter to a detector, the light beam being exposed to open air. When a raindrop falls into the path of the light beam, the light beam becomes, to some extent, obstructed, signaling the presence of rain. A major disadvantage associated with this method is the possibility of other weather elements, such as dust that may fall into the path of the light beam, causing erroneous detection of rain.
The present invention overcomes the disadvantages of the prior art by analyzing optical images to detect moisture on a surface such as a windshield of an automobile. More specifically, the present invention provides a sensor that can be mounted on a vehicle, such as the windshield of the vehicle. The sensor includes an optical image detector and a microprocessor with supporting control circuitry. The optical image detector acquires two-dimensional optical images from either the vehicle itself or an area surrounding the vehicle (e.g., the road ahead of the vehicle). The acquired optical images are then delivered to the microprocessor, which analyzes the image to determine whether moisture (such as rain) exists on the vehicle. Upon detection of sufficient moisture on the vehicle, the microprocessor circuitry can determine and cause the appropriate course of action such as activating windshield wipers by sending a signal to the vehicle windshield wiper control circuitry.
As indicated above, an application of the present invention is providing feedback to a the windshield wiper control circuitry of a vehicle. In a conventional vehicle with windshield wiper controls, a user can choose to activate and operate the windshield wipers on a periodic or intermittent basis. For instance, the user may adjust the settings of the windshield wiper controls such that the wipers are activated once every thirty seconds. The intermittent control function may also be speed dependent (i.e., the intermittent intervals may shorten as the vehicle increases in speed). In a typical rainstorm, the user normally adjusts the interval settings to shorter periods of time between windshield wiper activation if the rainfall becomes heavier, and adjusts the interval settings to longer periods of time between windshield wiper activation if the rainfall lightens.
In contrast, the present invention may provide feedback signals that can automatically adjust the windshield wiping functions based on the amount of moisture detected on the windshield. Hence, rather than the user guessing an appropriate time interval for the windshield wiper settings or having to adjust the interval settings in the event precipitation level changes, the present invention activates the windshield wipers whenever sufficient moisture on the windshield accumulates. Hence, an advantage of the present invention is to provide a more functional and accurate intermittent windshield wiper control that also relieves the user of the burden of constantly adjusting the windshield wiper settings as the amount of precipitation varies. It is noted that the present invention may also have application in controlling other application such as headlight or window wipers.